A mobile communication network comprises portable devices, such as cell phone, in radio communication with fixed base stations. These base stations comprise in particular antennas having a more or less large coverage. The coverage areas depend amongst other things on the emission power. The macro cell covers a broad area and may communicate with a large number of portable devices, whereas the micro cell cover a small cover and can manage a small number of portable devices. The radio network is thus arranged hierarchically: the macro cell ensures the coverage of a large area and the micro cell ensures a high capacity of communication with the cell phones. According to the characteristics of the area and in particular of the population density and it is advantageous to increase the number of micro cells in order to offer a better capacity in this area.
The radio coverage of each micro cell is managed by a device called “eNodeB” in the Long Term Evolution (LTE) technology. This device consumes energy. In certain cases, the eNodeB is switched on but does not manage any communication with portable device, for example during the night in residential zone, when the activity of the portables is very limited. Most of time and power of the eNodeB are thus consumed for nothing.
To save energy during low load period, it seems relevant to switch off cells—for example one or multiple micro cells are switched-off while the macro cells remain intact in order to avoid any coverage holes. In dense deployments, the number of unused micro cells being high, such solutions can lead to substantial energy savings. This will introduce a decrease of available network capacity. An important issue is to decide which micro cells to switch off such that coverage areas with mobile subscribers do not suffer from an undue reduction of capacity. Inversely, when the need for capacity increases, we need also to decide which micro cell to switch on to provide required capacity.
A solution consists in the macro cell managing all the portable devices when the traffic is low. However, the capacity of the macro cell can very quickly become insufficient when the portable devices in Idle mode become active, i.e. when they enter into communication. Another solution consists in switching on uniformly one micro cell out of two, one out of three etc. . . . , proportionally to the actual traffic load. But this empirical method may cause call drops and low quality of service in the radio communication network. The problem when choosing the cell to switch off using actual traffic load generated by the “active users” is that the reduced capacity may be not enough to serve portable devices in Idle mode already attached to this cell that when such UEs become active.
When the portable device is in Idle mode, it is difficult to locate it because it does not emit signal. It is easy to count the number of cell phones in active mode, but it is difficult to determine the number of portable device in Idle mode per base station . . . . In fact, the idle mode procedure implemented in the LTE standard does not permit to know how many terminals in idle mode are under the coverage of a given eNodeB. In fact the portable device is registered to the MME and the eNodeB has no context information. The only geographical information we have on the terminal is at the granularity of the Tracking Area, as the portable device performs Tracking Area updates when moving and also periodically when not moving. The radio network cannot decide optimum number of switched on micro cell in order to offer a sufficient capacity for the active portable devices and the portable devices in Idle mode which could wake-up
This granularity of the Tracking Areas doesn't give enough information of the number of UEs in idle mode under the coverage of an eNodeB.
The present invention allows among others advantages of estimating the number of portable devices within a zone and of determining the number of switched on micro cells to ensure the potential requests for traffic